By enabling the check min/max duration option in the Booking Form settings, the calendar in frontend will show the dates which are no longer available, including the minimum/maximum duration.
For example, customer A has booked the Amsterdam Room from 12 July to 18 July. The minimum duration to book this room is 3 days, therefore it is not possible for Customer B to book the room from 10 to 18 July, considering the minimum of 3 days plus the booked period.
If you disable the option, the customer will see the calendar with the dates available/unavailable, however, it does not take into consideration the minimum and maximum duration of the room. Therefore the days prior to the reservation will appear clickable in the calendar, even if the booking is not available on those dates.
If the customer wants to book the room from 10 to 14 July, he will get a message notifying that it is not possible to book this room in the period he wishes.